Suppose that items belong to to one of two possible classes, C =0, 1 (0="negative", 1 = "positive"). Suppose that some feature X is known (measured) for each item, but the class membership is unknown. Suppose that X| C = 0~ f0 (x) and X|C =1 ~ f1(x) (that is, f i (x) are the conditional densities of X given C= i). Consider the following classification function: